The present invention is related to a method for controlling a safety system in a vehicle and a control device.
Numerous methods and devices for controlling a safety system are known which are predominantly aimed only at the protection of the occupants of a motor vehicle using at least one impact sensor. Accordingly, an accident analysis is also usually conducted only from the standpoint of the timely activation of known occupant-protection equipment with the goal of effective absorbing the impact on occupants resulting from a change in vehicle speed due to an impact or an accident. Therefore, triggering strategies are regularly selected and implemented in the prior art on the basis of measured and/or calculated acceleration vectors in order to avoid, by the purposeful choice of occupant-protection equipment with a specifically directed effect. This is highly inadequate protection for the occupant(s) due to both too early and too late an activation of the appropriate airbags, seat belt tensioners and/or anti-rollover devices, etc. In addition to time-synchronized measurements of the transit time of signals relevant to accidents, approaches are also known for this purpose which use a large number of signal transmitters or sensors arranged in a distributed manner to locate the position of the damage and track the development of damage over time.
The starting point of these diagnoses with secondary strategies for triggering certain components of complex protection equipment is always an impact causing deformations involving at least the outer skin of a vehicle, as disclosed for example in U.S. Pat. No. 5,445,412 for a motor vehicle, and in German Patent Document DE 40 25 564 C1 for laminated fiber parts of an airplane. Methods are also known in this context in which an output signal of at least one sensor is subjected to frequency analysis, such as, for example, in German Patent Document DE 198 55 452 A1. Depending on an impact location, the spectrums caused by an impact have different effects between the front of the vehicle and the side of the vehicle due to the different bodywork structures. This property can be used for locating the site of an impact. Targeted protective measures are then triggered starting as of a predetermined accident severity that is given by an area of an envelope of the course over time of the sensor signal. In German Patent Document DE 100 34 524 A1, a defined frequency pulse is repeatedly emitted for excitation, with significant changes from a known spectrum being interpreted as an accident-caused deformation of the component or the monitored components of the vehicle. Finally, building on the use of a windowed Fast Fourier transformation for spectral analysis and evaluation of the relevance of a sensor interference signal for vehicle occupants, German Patent Document DE 100 12 434 A1 discloses a frequency analysis of the sensor signal by means of a wavelet transformation. Unlike a Fast Fourier transformation, a wavelet transformation also provides information on the occurrence in time of individual frequencies or frequency ranges.
German Patent Document DE 102 57 125 A1 describes a possible design for a sensor in the form of an piezo-electric film to detect pedestrian impact.
Methods which also offer the possibility of protecting pedestrians and/or bicyclists as early warning systems can be constructed on the basis of the methods and devices described above with only a very significantly limited maximum attainable protective effect. Based on the disclosure of German Patent Document DE 102 06 351 A1, a sensor in a particularly collision-prone area of a vehicle serves to detect a possible collision based on an initial physical contact of the vehicle with the object as a pulse-like excitation. A spectral distribution of the sensor signal with the pertinent amplitudes over the time, which is determined on the basis of a Fast Fourier transformation, can accordingly be used to distinguish between a collision with an human being and a collision with another object. Even this well-known method is not rapid enough with respect to the progress or course of an impact acting on the vehicle involved, and can have substantial weaknesses in terms of its robustness where the vehicle is coated with dirt, ice or snow and/or is hit by road debris.
It is therefore an object of the present invention to create a method with improved reliability for controlling a safety system in a vehicle that is effective for pedestrians and/or bicyclists.
In the method of the present invention for controlling a safety system in a vehicle, in which an output signal from at least one impact sensor is subjected to frequency analysis in an evaluation unit, which is integrated into an electronic control unit, the frequency analysis is performed in at least one predetermined frequency range. The spectrum of the output signal is compared with reference patterns. This takes into account the dependency of the spectrum on the current speed of the vehicle and/or on the current outside temperature of the vehicle. A control signal is generated from the control unit to trigger predetermined protective measures if an impact with a person to be protected (especially pedestrians and/or bicyclists) is detected with at least a predetermined probability.
The current velocity of the vehicle v and the outside temperature of the vehicle θ are given a special value. In both cases this involves easily measurable parameters, which are also conventionally recorded for other electronic control units in the vehicle. Vehicle velocity v is taken into account in the method of the present invention because there is a surprising influence on the sensor signal spectrum when there is a hard on soft and a soft on soft impact. It has also become known that the elements of a vehicle become less elastic as the outside temperature θ of the vehicle drops, so that a material that is soft under normal conditions reacts like a progressively harder material as the temperature drops. This is especially true for a soft outside bumper covering that is relatively soft under normal conditions. Taking at least one of these parameters into account therefore clearly increases the detection reliability of a method according to the present invention.
In a further development of the present invention, piezo-electric elements are used as sensors. The term piezo-electricity is understood to mean the property of some crystal structures to cause a charge separation on their surfaces under the effect of tension and pressure with the result that an electrical voltage can be tapped off via electrodes. With a suitable selection of material and corresponding shaping of the piezo-electric crystals, surface deformation and structure-borne noise effects can be converted over a wide frequency range into electrical signals via the associated mechanical deformations of a piezo-electric element. In addition to the use of piezo-electric crystals which can, for example, be designed as lead zirconium titanate or PZT bodies or as ceramic elements, the use of artificial piezo-electric films is well-known. The synthetics used usually involve highly polar substances which are subjected, as the film is manufactured in the warm state, to a highly static electrical field for uniform orientation of the molecules. In the course of cooling, this forced orientation of the molecules is almost solidly frozen in the film substance.
The materials mentioned above have in common that they can be used as passive sensors, with self-testing also being possible in a simple manner by making use of the reciprocity of piezo-electric materials with external active control and subsequent evaluation by a central system unit. For this purpose, the sensor element is therefore first controlled as an actuator, with the mechanical oscillation thus excited again being sensed as an electrical signal if the element is working without interference. This sensing can be performed by the sensor operated exactly as an actuator just as by at least one adjacently arranged sensor. This makes it possible for each sensor of a sensor field to be checked and monitored at any time for its operating properties with no additional expense for equipment like signal transmitters, etc.
In addition to the self-test of a particular sensor, however, a mechanical oscillation can also be imposed on a system to be safeguarded or monitored by the actuator operation, with an analysis of the oscillation created being subsequently provided by the same element with the properties of this system response being examined in an evaluation unit of the actual safety system. In addition to deformations of the material, cracks and other disturbances can also be detected in this way, especially by a frequency pattern that deviates from this system response. Thus, the present invention provides a method for operating a sensor with a reciprocal mechanism of action in a safety system, and offers the advantages of reliable self-testing. The present invention also provides the advantage of safety testing and system analysis provided at minor expense and with negligible interference in an overall mechanical system to be monitored, and with a diagnosis to complete each test. Prior damage of certain parts inside a motor vehicle can thereby be detected at any time and can be taken into account as well during the analysis of a possibly currently occurring accident, since each type of prior damage causes either a softening of parts of the frame or stiffening but in each case a deviation from unimpaired normal behavior.
In accordance with an exemplary embodiment of the present invention, a safety system comprises a large number of sensors, which are distributed over a structure to be protected as an observation area. The mechanical structure to be observed, such as for example a bumper or fender, can also be covered in a certain sense with a network of sensors, with the shape of the arrangement taking into account the particular type of mechanical structure and the location of the cluster points of possible accidental contacts with pedestrians and/or bicyclists by the way the sensors are distributed and the density of their distribution. Other points of use on a motor vehicle may, for example, also be trim work, especially in the area of the vehicle doors. Also in this arrangement, self-testing is still possible in the way described above via evaluation of a particular oscillatory reaction after an active test excitation by means of a predefined test signal and a recorded measurement signal. It is now also possible, by active excitation via a sensor and evaluation of the measurement signals received from all sensors, to perform a surface-covering evaluation for the analysis of errors and/or interference. All sensors can be constructed and attached in the same way, and can therefore belong to one series or one model of sensors.
Placement of the sensors with a permanently reliable attachment can be done individually or in the form of prefabricated groups at any time, even later, by embedding, adhering, screwing on, or the like, at certain points. To this end, bumpers or fenders, trim work, especially in door areas, roof areas and an engine hood and/or trunk lid are especially suitable locations on a motor vehicle for constructing a system according to the present invention.
In the event that non-harmonic oscillations develop, as, for example, in the case of impact with a foreign object or a pedestrian, precise identification of a particular event and location of its position are possible via the particular sensor elements. Accordingly, an evaluation of the intensity of the particular output signals is performed, which can be linked with a measurement of signal-transit time. Taken together, these rapidly give a reliable picture of an impact with a conclusion about the location or locations of the impact and the type of object or human being with which there has been an impact.
Suitable counter or protective measures can then be specifically triggered by subsystems which are incorporated in the safety system as a whole. This involves a targeted and precisely defined triggering of outside airbags in the area of the front of the vehicle, the windshield wiper mechanisms and/or the roof area near a rain gutter and/or a roof rail. As desired, adjustment of the hood to improve an angle of impact and to create a softer impact area with an enlarged crumple zone may also be considered. The triggering of seatbelt tensioners, various airbag systems or other active safety components can also be provided inside the vehicle in the event that danger to the occupants can no longer be ruled out. This is also regularly the case outside the range between 20 to approx. 50 kilometers an hour, for example, in accidents with wildlife, since the main impact point, especially with deer or elk, but also with large dogs, cows or horses, is still above the hood. This kind of animal therefore hits the windshield usually with no brakes being applied and very often breaks through it due to its own body weight. This poses extreme danger to the driver and any passenger so that active protective measures must be adopted here for occupants as well.
A method according to the invention is therefore also distinguished in its developments in that the use of robust, overload-resistant, cost-effective sensors that can be safely used over a wide temperature range and are capable of self-diagnosis, allows rapid and very reliable recognition of accidents with a pedestrian or bicyclist.